Electronic amplifier



April 17, 1956 A. v. HOLLENBERG ELECTRONIC AMPLIFIER 3 Sheets-Sheet 1Filed Jan. 7, 1950 //vv/v TOR A. M HOL L ENBERG ATTOR EV April 17, 1956A. v. HOLLENBERG 2,742,588

' ELECTRONIC AMPLIFIER Filed Jan. 7, 1950 5 Sheets-Sheet 2 FIG. 2

lNl/ENTOR A. 1 HOLLENBERG ATTORNEY I5 Sheets-Sheet INVENTOR A. V.HOLLENBERG w 0 0 %0 4 0 0 010 0 0 00 000 0 000 000 000 03%un$$-$wwwwnowwvvvvvm A 8 av April 7, 1956 A. v. HOLLENBERG ELECTRONIC AMPLIFIERFiled Jan. 7, 1950 NI" 0 N 7 2,742,588 ELECTRONIC AMPLIFIER ViHollenberg, Morris Plains, N. J., assignor to Bell TelephoneLaboratories, Incorporated, New York,

N. Y.,' a corporation of New York t. 3 Application January 7, 1950,Serial No. 137,315

' 14'Claims. c1. 3153.6)

, This invention relates to electronic devices utilizing extended hollowelectron beams and particularly to high frequency amplifiers of thetraveling-wave type inwhich 'a'defined beam of electrons travels forsome distance near a metallic circuit such as a helix in whichanelectromagnetic wave travels at a speed suitably related to that of theelectrons in the beam and in which the wave is ampli;

fied in its travel by virtue of interaction with the electron beam. TAn'objective of the invention is to provide improved operation oftraveling-wave amplifiers of the type employ.- ing a tubular electronbeam.

'Another' objective is to reduce the amplitude of unwanted noise signalcomponents generated within such amplifiers.

Another objective is to provide a means generally useful for reducingthe accumulation of positive ions in long 1 hollow electron beams.

In the operation of traveling-wave amplifiers in which an electron beamtravels for a considerable distance, it

has been ,found that unwanted signal components, which appear as noisein the output circuit, are generated within 9 the device which areapparently due to a concentration of positive ions in the region of theelectron beam where there is'a space charge depression of potential- Theions may be produced fromcollisions between electrons in the beam andmolecules of residual gas within the device.

' According to this invention this difficulty with noise signalcomponents in the output of the amplifier is over.- come by the use of acylindrical or helical conductor placed within and coaxial with thehollow beam and'the helix or. other circuit which conveys the electricalwave signal. This cylindrical or helical central conductor'is maintainedat a potential difierent'from that of the wave circuit so that atransverse electrical field is produced across the space between thecircuit and the-central conductor, and if the circuit is a helix thefield will extend betweenthe turns of the helix. The electron beam istubular and is coaxial with the circuit and the central conductor and,in a preferred design, passes longitudinally in the space between them.The beam is, therefore, in the trans verse electric field between thecentral conductor and the the-transverse electric field issufiiciently-intense the positive ions are drawn out of the region ofdepressed potential in the electron beam, thus reducing the amplitude ofthe unwanted electricalnoise signals due to the concentration of theions in the region of the beam.

I ...Wh'le theintroduction ofa. central conductor'make possible theapplication of the transverse field, forion' removal, it may withoutproper precautions introduce dif- 2,7 42,588 Patented Apr. 17-, 1956ficult-ies of aditferent sort; The presence of a conductor in the highfrequency field of the signal wave in the elec= tromagnetic circuit maymodify the field in an undesired resistance moderately'low as by makingitin the form of a corev of ceramic or other insulating material onwhich a helix of fine wire has been wound. The use of the highresistance or high impedance central conductor for removing positiveions from a tubular electronbeam and thereby reducing the amplitude ofunwanted electrical noise signals without adversely affecting theoperation of the traveling-wave amplifier is, a particular feature ofthis invention.

The invention and its application in'specific embodiments; will beunderstood from the following description and the'accompanying drawings,of which: I

Fig.1 shows a traveling-wave amplifier incorporating the inventionthrough utilization of a central conductor forv ion removal in the formof a high resistance rod;

Fig.2 shows an amplifier similar to that of Fig. l but employing a'central conductor for ion removal in the form ofa helix; and v Fig. 3illustrates an embodiment of the invention in a traveling-wave amplifierwhich is divided in the center and assembled in sections. It shows twosections of central conductor for ion removaland as an example the highresistance rod type of conductor is shown.

-In Fig. 1 the vacuum-tight envelope 1 is of non-magnetic metal andcontains the elements of the traveling-wave amplifier. Otherembodimentsof the invention may employ a non-metallic envelope, such as glass, inwhich case means for supporting and connecting to the helix other thanthose to be described may be employed. Elements of the tube areconnected outside of the envelope by leads .passingthrough glass orceramic seals 2, 3, 4, and 5. v The ring-shaped indirectly heatedcathode 6, the heater for .whichisnot" shown, emits a tubular beam ofelectrons 12, the flow of which is controlled by grid 7 which isvariably biased with respect to the cathode by battery 10. The electronbeam'is accelerated by grid 8 connected to the metal envelope -1 andthereby to the accelerating potential source, battery 9. Transversemotion of the electrons is restricted by a longitudinal magnetic fieldproduced by currentflowing in the solenoid 11 and the beam of electronsis, therefore, tubular in shape throughout the length ofthe tube. Thedirect current for the solenoid, 11 may be supplied from any suitablesource (not shown). The electron beam travels within the helix 13 intheregion close to the wiresof the helix where the amplitude of the highfrequency field of the signal is large. The helix is supported byceramic rods 14 which may be supported directly by the metal envelope asshown or indirectly by two metal collars attached to the rods andsupported by the envelopen- -The turns of the helix are maintained inproper spacing by a series of notches ground into the supporting rods'14 into which the helix wires are bound by glazing material. Highfrequency loss is introduced into the central portion of the helix bymeans of a thin coating of conducting material such as graphite on thesupporting rods in the. central region as indicated at 15. The thicknessof the coating is gradually increased from each end toward the center inorder to prevent reflection of the signal wave. The graphite coatingattenuates all signal waves passing this region except those carriedinthe electron beam. Input signals on the coaxial line 16 are applied tothe helix 13 through capacitor 17 and a connection at point 18 on thehelix. The location of point 18 and the capacitance of capacitor 17 arechosen to apply the signal wave to the helix atthe operating frequencywithout reflection. The input end of the helix wire is connected, atpoint 19, to the metal envelope which also forms the outer conductor ofthe coaxial line 16. At the output end of the helix, identicalarrangements are made for extracting the signal wave at point 20 throughcapacitor 21 into output coaxial line 22, with connection of the end ofthe helix wire to the metal envelope and outer conductor of the coaxialline at point 23. The electron beam 12 is collected by collector 24'which is maintained at an appropriate potential by battery 9. Theion'removing central conductor 25 is supported on the axis of the helix13 by suitable means, not shown, which may be insulatorswhich supportcollars 26 and 27 from grid 8 and collector 24, respectively, orotherappropriate insulating supports. Connections may be brought out from oneor both ends of the central conductor. Connections from both ends areshown in Fig. 1 and these are brought to a common point on battery 9which maintains the central conductor above or below the potential ofthe helix depending upon the position of the connection to the battery.With the connection shown in Fig. l the central conductor is at a lowerpotential than the helix which is the preferred method of operation.However, the conductor may be operated at a potential higher'than thehelix.

The ion removing central conductor 25 shown in Fig. l is of the highresistance type utilizing in its construction a rod of ceramic materialhaving a small diameter. A rod of .OSS-inch diameter has been used. Forthe metallic collars 26 and 27 molybdenum has been used; These collarsclosely fitting the ceramic rod are attached near the two ends of therod and are held in position by a glazing paste which is applied to theassembly, the assembly then being heated in a reducing atmosphere untilthe paste melts. On cooling, the melted glazing paste becomes a firmglass bond holding the collars in place. Electrical connections are madeto one or both of the metal collars. The region between the collars 26and 27 is covered uniformly with a thin layer of conducting material,for example graphite which in suspension form may be applied to thisregion by spraying, the spray overlapping the metal collars. The amountof material deposited may be measured if the deposit is uniform, by

measuring the electrical resistance between the metal collars; and thismeasures the property of the conductor which must be properly chosen topermit the conductor to serve its purpose of drawing out positive ionswithout materially disturbing otherwise the operation of thetraveling-wave amplifier. The resistance per unit length of the coatingshould be high enough that the electric field of the signal wave is notdistorted or unduly attenuated. It must be low enough to allow thepositive ions collected by the central conductor, when his negative withrespect to the circuit, to flow out without accumulation and resultinglarge change of potential of the conductor. Ion currentswhich have beenobserved under circumstances similar to those of a traveling-wave tuberoughly 25 centimeters long are a few microamperes in magnitude. A totalresistance in the central conductor'of one megohm (which amounts to40,000 ohms per centimeter) will under such a condition lead topotential-differences between the ends of the central conductor orbetween the endsand the center of at most a few volts which is notbelieved injurious. On the other hand, the power absorbedin the centralconductor from-the high frequency field of the signal wave in the helixmust be considered. It is desired that the resistance in the centralconductor be sufficiently high that the total attenuation in thelengthof the tube is not large compared with the total gain otherwise tobe expected from the device. Estimates of typical cases show that atotal resistance of the order of one megohm for the central conductor 25is also satisfactory on this basis. A total resistance, uniformlydistributed, of about one megohm for the central conductor may,therefore, satisfy both requirements. Circumstances may, of course,dictate a different value of resistance for the central con ductor.Therefore it is not intended to limit the value of resistance other thanis required to avoid excessive direct-current potential gradient alongthe conductor or excessive attenuation of the high frequency wave.

The enclosure within the envelope 1 of Fig. l is evacuated in the usualmanner and sealed off at the tubulation 28. lmpedances and by-passcondensers or other means according to common practice may be associatedwith the external leads to the electrodes of the amplifier tube in orderto prevent high frequency feedback along the connections to the batteryor other undesired effects-of the presence of high frequency voltage onthe leads.

Fig.2 shows the use of a central ion removing conductor in helical form.The conductor may be made in this form by winding a fine wire, forexample tungsten or molybdenum wire, on an insulating rod of ceramic orother suitable material. In Fig. 2, all of the elements 1 to 24 and 26to 28 are the same as in Fig. 1. The central conductor 29 is in helicalform wound on a ceramic rod of small diameter to the ends of whichmetallic collars 26 and 27 are attached as in the showing of Fig. landwhich may be supported as suggested for Fig. 1. Theends of the wire ofthe helical central conductor are connected tothcse collars 26 and 27.The Wire may be of 0.001-inch diameter and wound 500 turns per inch. Itis desirable to make'the diameter of the helix of the central conductorsmall, for example 0.060-inch diameter. With the dimensions given, thevelocity of propagation of a signal wave along the axis of the helicalcentral conductor will be roughly of the speed of light. Equality ofvelocities of propagation in the outer signal wave carrying helix and inthe helical central conductor probably leads to coupling between thehelices and therefore absorption of power in the helical centralconductor and should be avoided. The velocity resulting from the abovegiven dimensions is smaller than that usually found useful intraveling-wave tubes. The direct-current resistance of the wire of thehelical central conductor of the dimensions given is only a few thousandohms for wire material such as tungsten and molybdenum. Large currentsthan mentioned in connection with Fig. l, of the order ofonemilliampere, for example those which result from partial interceptionof'the electron stream by the conductor or its supports could therefore,be withdrawn by the centralzconductor, if necessary, without excessivevoltage drop. Whereonly small currents, of the order of microamperes,from the positive ions are expected, there is negligiblevoltagedifference/between the ends of the central conductor even if connectionis made only to one end as in Fig. 2. Connections may, of course, bemade to both ends as in Fig. l if desired.

Fig. 3 illustrates a modification of the structures shown in Figs. 1 and2 which performs the same functions and may employ either the highresistance central conductor of Fig. 1 or the helical type of Fig. 2.For a convenient examplethe high resistance type is shown in Fig; 3..The structure of Fig. 3 may, under some circumstances, possessadvantages of mechanical convenience in fabrication and assembly in thatthe lengths of the helix and central conductor which arerequiredto befabricatedin single units are half that required with the structures ofFigs. 1 and 2. It possesses also the featureofnattenuating morecompletely the signals crossing the central portion of the tube exceptthose carried in the electron stream.

In Fig. 3; the elements bearing the samedesignations as those in Fig. 1are identical, except'that the envelope 1 is assembled in sectionsinFig. 3, and perform the same functions as in Fig. 1. Thehelix whichconducts the electrical signal is in two sections 30 and 31. The ends ofthese sections in the central portion of thetube are supported so as tobe in alignment by members 32 and 33 attached. to therespective halvesof the envelope. The central conductor, of either high .resistance, as.shown, or helical form is in two portions 34 and 35. The ends in thecentral portion. of the tube are supported by members 36 and 37, whichare thin to avoid interception of more than a small portion of the beamcurrent, and are attached to members 32 and 33. As in Figs. 1 and 2 thincoatings of conduct- .ing material are deposited on the support rods 41and 42 of the signal wave carrying helices30 and 31 in the regions 39and 40 with thickness gradually increasing toward the center of the tubein-order to terminate the two helix sectionswithout reflection. The twohalves of the tube are competely assembled independently and finallyjoined together by ring 38 so that the complete envelope is vacuumtight.Y

As has been stated above, the central ion removing conductor orelectrode may be maintained either above or below the potential of theconductor of the electrical signal wave circuit, though it is believedpreferable .to

maintain the central conductor at the lowerpotential.

. Also, it is not without the scope of the invention to use the centralion removing conductor with a helical signal wave circuit which iswithin the hollow electron beam rather than external to thebeam as shownin the three figures. In that case the withdrawal of positive ions fromthe electron beam would depend upon the lines of force of the transversefield between the central conductor and the helix of the signal wavecircuit which extend through between the turns of that helix as far asthe outside electron beam. The arrangement with the electron beambetween the central conductor and the circuit helixas shown in all threefigures is believed preferable. V a, i

It is not intended that the scope of the invention'be limited to thefield of traveling-wave amplifiers as obvviously the central ionremoving conductormay be employed in other devices employing hollowelectron beams from which it is desired to remove positive ions.

What is claimed is:

1. An electronic device comprising an evacuated envelope containing anelectron emitter and an electron collector spaced apart, beam focusingmeans for'form: ing a tubular-shaped beam of electrons in which theelectron paths are substantially parallel to the axis be- .tween saidemitter and said collector, electric potential means connected to saidemitter, collector and beam focusing means for moving the electronsalongzsaid paths, anelectrical wave transmission circuit whereby an ap.plied wave is amplified as it travel therealong comprising a helicalcoil coaxial with and extending along external .to said path of thetubular electron beam, an electrical conductor in the form of a helixand having; a high impedance at the operating frequency of the wavetransmission circuit substantially coaxial with and extending alongwithin said path of the tubular electron beam, and electric potentialmeans connected to said conductor for maintaining it at a direct-currentpotential substantially different from that of said helical coil ofthe-wave transmission circuit.

2. An 7 electronic device comprising an evacuated envelopecontaining anelectron emitter and an electron collector spaced apart, beam focusingmeans for forming '-a tubular-shaped beam of electrons in which theelec- V tron paths are substantially parallel to the axis between saidemitter and said collector, electric potential means connected to saidemitter, collector and beam focusing means for moving the electronsalong said paths, an electrical wave transmission circuit whereby anapplied wave is amplified as it travels therealong comprising a helical,coil coaxial with and extending. along {said path of 'the tubularelectron beam, an electrical conductor in the form of a helix and havinga high impedance at the operatingfrequency of thelwave transmissioncircuit substantially coaxial with and extending along within said pathof the tubular electron "beam, and electric potential means connected tosaid conductor for maintaining it at a direct-current potentialsubstantially different from that of said helical coil of the wavetransmission circuit. 3 l

3..An electronic amplifier comprising an evacuated envelope containingan electron emitter and an electron collector spaced,apart,- beamfocusing means for forming a tubularsha'ped' beam of electrons in. whichthe electron paths are substantially parallel to the axis between saidemitter' and said-collector, electricpotential means-connected to saidemittergcollector and beam focusing meansfor moving theelectro'ns alongsaid paths, an electrical wave transmissioncircuit whereby an appliedwave is amplified as it travels therealong'comprising an electricalconductor extending along said path of the tubular electron beam inproximity thereto, an electrical conductor in the form of a helix andhaving a high impedance at the operating frequency of the wavetransmission circuit extending alo'ng within saidpath of the tubularelectron beam substantially along the axis thereof and electricpotential means connected to said con ductors for maintaining asubstantial direct-current difference of potential between them'.' I 14. An electronic device comprisingjan evacuated envelope containing anelectron emitterand anelectron collector spaced apart, beam-focusingmeans for forming a tubular-shaped beam of electrons in whichthe-electron paths are substantially parallel to the between saidemitter and said collecton electrical potential means connected to saidemitter, collector and beam focusing means for moving the electronsalong-said paths, two sections of electrical wave transmission circuitwhereby a wave is amplified asits travelstherealong each comprising ahelicalcoil, the two coils beingcoaxial with and extending alongdifierent portions -of said path of the tubular electron beam, twosections of electrical conductor eachin the form of a helixandhaving ahigh impedance at the operating frequency of the wave transmissioncircuitv and being'located substantially coaxial with and extendingalong within said path of the tubular electron beam, one of saidsections of conductor being within each of said sections of-wavetransmission circult, and potential means connected to, said conductorsections for maintaining eachat a direct-current potential substantiallydifierent from that of the coil of the wave transmission circuit withinwhich it is located. v

5. A device according to claim 1 in. which the high impedance electricalconductor comprises a helical coning a wave propagation velocitysubstantially less than ,the wave propagation velocity of the said wavetransmission circuit.

8. ,An electronic device comprising an evacuated envelope'containing anelectron emitter and an electron collector spaced apart, beam focusingmeans for forming a tubular-shaped beam of electrons in which theelectron paths are substantially parallel to the axis between saidemitter and said collector, electric potential means connected to saidemitter, collector and beam 2,742, ass

focusing means for moving the electrons along said paths, an electricalwave" transmis'sion circuit whereby an applied wave is amplified as ittravels therealong comprising a helical coil coaxial with and extendingalong external to said path of the tubular electron beam, an electricalimpedance means capable of conducting direct current, in the form of ahelix and having substantial impedance at the operating frequency of thewave transmission circuit substantially coaxial with and extending alongwithin said path of the tubular electron beam, and electric potentialmeans connected to said impedance means for maintaining it at adirect-current potential substantially different from that of saidhelical coil of the wave transmission circuit.

9. An electronic device comprising an evacuated envelope containing anelectron emitter and an electron collector spaced apart, beam focusingmeans forforming a tubular-shaped beam of electrons in which theelectron paths are substantially parallel to the axis between saidemitter and said collector, electric potential means connected to saidemitter, collector and beam focusing means for moving the electronsalong said paths, an electrical wave transmission circuit whereby anapplied wave is amplified as it travels therealong comprising a helicalcoil coaxial with and'extending along external to said path of thetubular electron beam, and'electrical impedance means capable ofconducting direct current, in the form of a helix, substantially coaxialwith and extending along within said path of the tubular electron beam,and electric potential means connected to said impedance means formaintaining it at a direct-current potential substantiallydiiferentfrom' that of said helical coil of the wavetransrr'iissioncircuit.

10. An electronic device comprising an evacuated envelope containing anelectron emitter and an electron collector spaced apart, beam focusingmeans for forming a tubular-shaped beam of electrons in which theelectron paths are substantially parallel to the axis between saidemitter and said collector, electric potential means connected to saidemitter, collector and beam focusing means for moving the electronsalong said paths, an electrical wave transmission circuit whereby anapplied wave is amplified as it travels therealong comprising a helicalcoil coaxial with and extending along said path of the tubular electronbeam, an electrical impedance'means capable of conducting directcurrent; in the form of a helix and having substantial impedance at theoperating frequency of the transmission circuit substantially coaxialwith and extending along within said path of the tubular electron beam,and electricpotential means connected to said impedance means formaintaining it at a direct-current potential substantially differentfrom that of said helical c'oil'o'f the wave transmission circuit.

11. An electronic device comprising an evacuated envelope containing anelectron' emitter and an electron collector spaced apart; beam focusingmeans for forming a tubular-shaped beam'of electrons in which theelectron paths are substantially parallel to the axis between saidemitter and said collector, electric potential means connected to saidemitter, collector and beam focusing means formoving the electrons alongsaid paths, an electrical wave transmission circuit whereby an appliedwave is amplified as it travels therealong comprising a helical coilcoaxial with and extending along said path of the tubular electron beam,an electrical impedance means capable of conducting direct current, inthe form of a helix, substantially coaxial with and extending alongwithin said path of the tubular electron beam, and electric potentialmeans connected to said impedance means for maintaining it at adirect-current potential substantially different from that of saidhelical coil of the wave transmission circuit.

12. An electronic amplifier comprising an evacuated envelope containing"an electron emitter and an electron collector spaced apart, beam.focusing means for forming a tubular-shaped beam of electrons in whichthe electron paths are substantially parallel to the axis between saidemitter and said collector, electric potential means connected to saidemitter, collector and beam focusing means for moving the electronsalong said paths, an electrical wave transmission circuit whereby anapplied wave is amp'lifiedas it travels therealong comprising anelectrical conductor extending along said path of the tubular electronbeam in proximity thereto, a second electrical conductor extending alongwithin said path of the tubular electron beam substantially along theaxis thereof, said second electrical conductor being in the form of awavetransmission line having a wave propagation'velocity therealongsubstantially less than the wave propagation velocity of said wavetransmission circuit, and electric potential means connected to saidconductors for maintaining a substantial direct-current difference ofpotential between them.

13. An electronic device comprising an evacuated envelope containing anelectron emitter and an electron collector spaced apart, beam focusingmeans for forming a tubular-shaped beam of electrons in which theelectron paths are substantially parallel to the axis between saidemitter and said collector, electrical potential means connected tosaid'emitter, collector and beam focusing means for moving the electronsalong said paths, two'sections of electrical wave transmission circuitwhereby a wave is amplified as it travels therealong each comprising ahelical coil, the two coils being coaxial with and extending alongdilferent portions of said path of the tubular electron beam, twosections of electrical conductor located' substantially coaxial with andextending along withinsaid path of the tubular electron beam, one ofsaid sections of conductor being within each of said sections of wavetransmission circuit, each said section 'of conductor being in the formof a helix and having an impedance at the operating frequency of thewave transmission circuit which for a given length along the wavetransmission circuit is higher than the similar impedance of the wavetransmission circuit, and potential means connected to said conductorsections for maintaining each at a-direct-current potentialsubstantially'differ'ent from that of the coil of the wave transmissioncircuit withinwhich it is located.

14. A' traveling wave vacuum tube comprising means for generating a'hollow tubular electron beam for flow along a given path, a wavepropagating circuit in the form of a helically wound conductor extendingalong and coaxial with said beam path, an electrode in the form of ahelically wound conductor extending along inside of' and coaxial withsaid beam path and having awave propagation velocity therealongsubstantially less than the wave propagation velocity along said wavepropagating circuit, and means electrically connectedto said'circuit andsaid electrode to apply thereto adifierence of' direct currentpotential.

References Cited in the file of this patent UNITED STATES PATENTS2,005,330 Sukumlyn June 18, 1935 2,064,469 Haeff Dec. 15, 1936 2,122,538Potter July 5, 1938 2,264,495 Wilner Dec. 2, 1941 2,541,843 Tiley Feb.13, 1951 2,610,308 Touraton et al Sept. 9, 1952

